These routines require that the rpc.rusersd(1M) daemon
be configured and available on the remote system indicated by host. The rusers() protocol is used to retrieve information about users logged in on the remote
system.

rusers() fills the utmpidlearr structure with data about host, and returns 0 if successful. up
must point to an allocated utmpidlearr structure. If rusers() returns successful it will have allocated data structures within the up structure,
which should be freed with xdr_free(3NSL) when you no longer need them: